1. Field of the Invention
The invention relates to a method of injecting a product into a first fluid, whereby in an injection apparatus having a substantially disc-shaped rotor, a radial displacement effect is imparted to the first fluid, said product being injected into a limited intermediate zone above the disc-shaped rotor displaced from both the center and the circumference of the rotor, in which zone the first fluid is exposed to a tangential dispersion effect in addition to said displacement effect.
2. Description of the Related Art
Such an injection method is known from published international patent application WO 94/13395.
Without in any manner being restricted thereto, the method according to the invention has substantial fields of application in, partly, heat treatment of liquids by injection of steam. For example, bactericidal UHT treatment of milk products or pregelatinization of starch products, partial injection of gases, for example CO.sub.2 or nitrogen into such liquids which are subsequently to be spray dried with the aim of reducing the density of a powder product obtained by the spray drying, partial injection of a liquid, for example water, into certain fatty or oily products with a view to reduction of the fat content and partly mixing of a solid product in powder or granulate form into a liquid.
In connection with the spray drying of food products, for example milk products or fruit juice, it is known from U.S. Pat. Nos. 3,185,580 and 3,222,193 to inject a gas directly into an elongated mixing pipe through which the liquid starting material flows before supply to an atomizer in the spray drying apparatus. This type of gas injection is not suitable for heat treatment at higher temperatures, as it will inevitably lead to burning. Actually, the above patents also direct that a heat treatment of the product, for example for pasteurization purposes, be made in a conventional preheater.
U.S. Pat. No. 3,182,975 describes an apparatus for heat treatment of milk products at an increased temperature after prior preheating by injection of steam into a mixing chamber to which the product to be treated is supplied. Steam injection is carried out by means of a propeller-like rotor with perforated tubular blades where the steam extravasates on the back of the rotor blades seen in the direction of rotation at a relatively low pressure, whereby the pressure is increased through the mechanical influence from the rotation of the rotor. The intention is to obtain a rapid heating without burning.
SU patent specification No. 578046 describes another method of heat treatment of milk products where the product is also supplied to a mixing chamber by a propeller-like rotor. In the '046 specification the steam supply is made via a distributor system with annular distributing conduits arranged concentrically in relation to the rotor and controlled by means of a valve arrangement so that the steam in the central area of the chamber is supplied at a relatively low temperature and pressure, and in the peripheral area at a substantially increased temperature and pressure. The intention is to obtain a very rapid heating to sterilization level after a preheating in the central area. In this construction, however, the strong heat influence at the periphery involves a considerable risk of burning.
It is known from US patent specification No. 4,479,908 to inject gas into a fluid product of a higher density by a method in which a strong turbulence and high flow velocity are imparted to the fluid product by passing it through a conduit part with a curved wall in connection with a constricted flow section where the gas injection takes place through an adjustable nozzle. According to the patent, the method may also be used for heat treatment of milk products by injection of steam at a temperature of about 170.degree. C.
CH patent specification No. 531363 describes an apparatus for mixing a liquid raw material with a gas, for example with a view to foaming. Mixing takes place in a mixing chamber by means of a rotor disc with projecting teeth moving between stationary teeth in a surrounding stator part, the rotor disc performing an eccentric circulatory movement about the axis of the stator frame.
Similar embodiments of mixing heads with a rotor provided with teeth engaging with teeth in a stator system where the sets of teeth may be arranged in several steps mutually displaced in the radial and axial directions are known from DE patent No. 3127684, EP patent application No. 0253139 and published international patent application No. WO 91/07221.
Whereas, in the two latter mixing methods the supply of the fluid product to be treated, and the injection of gas take place at the same place in the mixing chamber, preferably in its central part, the method disclosed in DE-C-3127684 provides for injection of the gas into a working space displaced from the inlet and outlet and delimited by projecting toothed rims from the rotor and stator, respectively.